Color-proofing is the procedure used by the printing industry for creating representative images that replicate the appearance of printed images without the cost and time required to actually set up a high-speed, high-volume printing press to print an example of the images intended. One such color proofer is a lathe bed scanner which utilizes a thermal printer having half-tone capabilities. This printer is arranged to form an image on a thermal print medium, or writing element, in which a donor transfers a dye to the writing element upon a sufficient amount of thermal energy. This printer includes a plurality of writing diode lasers which can be individually modulated to supply energy to selected areas of the medium in accordance with an information signal for writing onto the writing element. A focusing laser beam is focused at the preceding position to which the writing laser beam is to write next (i.e., next printing location) for permitting adjustment of the focal point of the writing laser beam prior to its writing at the next printing location.
The writing element is supported on a rotatable imaging drum, and rests concentrically around the imaging drum with the ends of writing element positioned in a spaced apart relationship so that a portion of the imaging drum is not covered by the writing element, hereinafter referred to as the exposed portion of the imaging drum. A print-head includes one end of a fiber optic array having a plurality of optical fibers that are coupled to the writing diode lasers for transmitting the signals from the laser to the print head. The print-head with the fiber optic array is movable relative to the longitudinal axis of the drum. The dye is transferred to the writing element as the radiation, transferred from the diode lasers to the donor element by the optical fibers, is converted to thermal energy in the donor element.
The cylindrical-shaped imaging drum includes a hollowed-out interior portion and further includes a plurality of holes extending through its housing for permitting a vacuum to be applied from the interior of the drum to the receiver and writing elements for maintaining their position as the drum is rotated.
During the writing process, the print head emits the laser beam as it moves along the drum. The beam then passes through the donor element for causing the dye to transfer to the writing element.
Although the presently known and utilized scanner is satisfactory, it is not without drawbacks. The focusing laser beam is sometimes directed from the writing element, to the imaging drum and back to the writing element due to the fact that writing element does not cover the exposed portion of the imaging drum. This reflected beam causes the focusing of the writing laser beam to have transient oscillations which can create undesirable artifacts in the writing element.
Consequently, a need exists for improvements in the construction of the lathe bed scanner so as to overcome the above-described shortcomings.